1. Technical Field
This description generally relates to the field of wireless sensor nodes, and more particularly to monitoring environmental characteristics using wireless sensor nodes.
2. Description of the Related Art
Networks built from small nodes with sensing and wireless communications capabilities may be used to collect data in a variety of environments. Each wireless sensor node is typically an autonomous device that detects or monitors environmental characteristics of its surrounding environment. These wireless sensor nodes may then be organized into networks for data collection and delivery.
Such networks may be used in the performance of a number of tasks, including monitoring manufacturing facilities, infrastructure or construction sites; monitoring food, electronics or other sensitive items; tracking documents; detecting changing weather conditions or early warning signs for natural disasters; monitoring for home automation; etc. The wireless sensor nodes may be positioned at precise locations or scattered randomly throughout the monitored environments to detect characteristics including: temperature, density, strain, deformation, acceleration, pressure, opacity, concentration, chemical state, resistance, mildew, phase changes, humidity, etc. The wireless sensor nodes may be periodically or continuously queried to obtain information regarding past or current environmental characteristics.
The individual wireless sensor nodes may range from “macro-sized” wireless sensor nodes, from the size of backpacks to roughly the size of a coin, to “micro-sized” sensor nodes, that can be the size of dust particles. These wireless sensor nodes may communicate wirelessly in a number of ways, but most commonly communicate via electromagnetic radiation (e.g., radio or microwave wavelengths).
In one implementation, each wireless sensor node may include a radio frequency identification (“RFID”) transponder commonly referred to as an RFID tag. Such RFID tags typically employ an antenna coupled to a wireless transponder circuit to transmit and/or receive data via electromagnetic signals in some frequency range.
The wireless transponder circuit found in many RFID tags typically includes a memory portion and a logic portion. The memory portion stores data, while the logic portion controls the reading, writing, and manipulating of data in the memory portion. The logic portion may further couple between the memory portion and the antenna to act as a transmitter, receiver, or transceiver for reading and/or writing data to and/or from the RFID tags.
Active wireless sensor nodes may include a discrete consumable power source, such as a battery, to provide power to the wireless transponder circuit and the sensor. In contrast, passive wireless sensor nodes may derive power from a wireless interrogation signal, for example, by backscattering the signal as a response signal encoded with information from the wireless sensor node.